Ultrasonic energy is used in a variety of applications including, but not exclusive of, medical, industrial, and military applications. One common use for ultrasonic energy in manufacturing is for cleaning objects in liquids. In ultrasonic cleaning, a transducer, usually piezoelectric but sometimes magnetostrictive, is secured to or immersed in a cleaning tank to controllably impart ultrasonic vibration to the tank. The tank is filled with a cleaning liquid and parts are immersed into the liquid to be cleaned by ultrasonic agitation and cavitation. The ultrasonic energy itself can dislodge contaminants. Under certain conditions, the ultrasonic energy also creates cavitation bubbles within the liquid where the sound pressure exceeds the liquid vapor pressure. When the cavitation bubbles collapse, the interaction between the ultrasonically agitated liquid and the contaminants on the parts immersed in the liquid causes the contaminants to be dislodged.
In a typical ultrasonic cleaning system, the cleaning liquid is an aqueous solution, and parts immersed therein are cleaned via the aforementioned agitation and cavitation of the aqueous solution. Typically, the ultrasonic transducers transmit ultrasonic energy into the liquid-filled tank at frequencies of 18 kilohertz or greater, typically at a resonant frequency of the transducer and the load. The load includes the cleaning tank, the liquid in the tank, and the parts immersed in the liquid. When the ultrasonic transducer is driven at the resonant frequency of the load, the system is capable of delivering maximum power to the load.
Typically, ultrasonic transducers include a drive rod made from either piezoelectric, piezoceramic, or magnetostrictive materials, which oscillate with the frequency of the applied current or voltage. Magnetostrictive materials include aluminum and iron alloys or nickel and iron alloys. Both piezoelectric and piezoceramic materials have been known to fail due to the thermal and mechanical stresses produced during prolonged operation of the transducer. Because it is not always obvious when they occur, these component failures may not be discovered until the end of a lengthy cleaning process. In manufacturing, such failures can be costly, both in terms of the replacement cost of the failed components, and, just as importantly, in terms of the increased cycle time for those parts that cannot be processed until the transducer is repaired.
Additionally, there are also instances when the generator that supplies power to the ultrasonic transducers fails, resulting in a complete loss of power. If there is not an operator watching the tank at the time the generator failure, the loss of power may go undetected. This would result in lost production time and increased cycle times due to additional cleaning cycles.
To provide users of ultrasonic cleaning systems with some warning when an ultrasonic transducer or power generator fails, transducer fault indicators have been developed. However, conventional transducer fault indicators tend to be complex, costly, and may not always provide a simple and convenient method of signaling the user. Further, some conventional transducer fault indicators require stored current or voltage waveform information to serve as a reference against which a comparison of some monitored signal is made. Also, the functionality of some conventional transducer fault indicators may be limited by the normal current fluctuations seen in drive circuits for ultrasonic cleaning systems. Variations in the temperature and level of the cleaning fluid, along with the mass of the parts being cleaned can all affect the amplitude of the current signal supplied to the ultrasonic transducers. This current can vary by as much as 25%-30% as these factors tend to change the characteristics of the load placed on the power supply. Some conventional transducer fault indicators may not operate as intended with this amount of variation.
It would therefore be desirable to have a transducer fault indicator that does not require stored current or voltage waveform information to serve as a reference against which a comparison of some monitored signal is made, and which is not hampered by the normal current fluctuations seen in drive circuits for ultrasonic cleaning systems. Further, the device should be capable of detecting transducer or power generator failures either prior to, or immediately after, occurrence of the failure without the complex and costly circuitry typically found in conventional transducer fault indicators. Embodiments of the invention provide such a system. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.